Fiber-reinforced resin compacts are light in weight and excellent in strength, and hence have hitherto been favorably used for, for example, exterior finish of vehicles and ships. Recently, long-fiber-reinforced resin compacts have been known which are excellent in strength and modulus of elasticity due to the inclusion of reinforcing fibers having long filler length, and such compacts are often used for bumpers and bodies of vehicles. The long-fiber-reinforced resin compacts are generally formed by using long-fiber-reinforced thermoplastic resin preforms with an injection molding method or a stamping molding method.
Here, the long-fiber-reinforced thermoplastic resin preforms have pellet-like shapes or sheet-like shapes, and include glass fiber bundles cut to predetermined lengths as long fibers, wherein a thermoplastic resin is impregnated in the glass fiber bundles and at the same time allowed to be held around the glass fiber bundles. Such a long-fiber-reinforced thermoplastic resin preform can be produced as follows.
First, a glass composition as a raw material for the glass fibers is melted into a molten glass, and glass fiber bundles are prepared by bundling the continuous glass fibers spun from the resulting molten glass. Then, by allowing the glass fiber bundles to pass through the molten thermoplastic resin, the thermoplastic resin is impregnated in the glass fiber bundles and at the same time allowed to be held around the glass fiber bundles. Subsequently, by cooling the glass fiber bundles impregnated with the thermoplastic resin and allowed to hold the thermoplastic resin around the glass fiber bundles and by cutting the cooled glass fiber bundles to a predetermined length, the long-fiber-reinforced thermoplastic resin preform having a pellet-like shape can be obtained. By dispersing thinly and uniformly the pellet-like long-fiber-reinforced thermoplastic resin preform and by thermally fusing the resulting dispersed resin preform, a sheet-like long-fiber-reinforced thermoplastic resin preform can be obtained.
As the glass fibers, usually glass fibers composed of E-glass are used; however, glass fibers composed of E-glass may not attain sufficient strength and sufficient modulus of elasticity. In this connection, glass fibers composed of S-glass, in place of E-glass, are known to have more excellent strength than the glass fibers composed of E-glass.
The glass fibers composed of S glass has a composition in which the content of SiO2 is about 64.0 to 66.0% by mass, the content of Al2O3 is about 24.0 to 26.0% by mass and the content of MgO is about 9.0 to 11.0% by mass, based on the total amount of the glass fibers. However, when a glass composition as the raw material for S-glass is melted into molten glass, and glass fibers are obtained by spinning the molten glass, S-glass has a problem that the 1000-poise temperature of the molten glass is extremely high, and additionally the difference between the 1000-poise temperature of the molten glass and the liquid phase temperature of the molten glass is small.
When the 1000-poise temperature of the molten glass is high, a high temperature is required in the process of melting the glass and the process of forming fibers from the glass, and hence a load due to thermal load on the production facilities is large. When the difference between the 1000-poise temperature of the molten glass and the liquid phase temperature of the molten glass is small, in the process during which the molten glass is spun and then cooled to be glass fibers, the glass fibers tend to undergo crystallization (devitrification) even under the effect of slight temperature decrease and a problem of breakage of glass fibers or the like tends to occur. Consequently, when the glass composition as the raw material for S-glass is melted into a molten glass, it is difficult to stably spin glass fibers from the resulting molten glass, and accordingly, it is also difficult to produce the long-fiber-reinforced thermoplastic resin preform by using S-glass.
The “1000-poise temperature” is an index of the standard when a molten glass is spun into fibers and means the temperature at which the viscosity of the molten glass comes to be 1000 poises. The “liquid phase temperature” means the temperature at which crystals start to precipitate when the temperature of the molten glass is decreased. The temperature range (working temperature range) between the 1000-poise temperature and the liquid phase temperature is a standard indicating the easiness in spinning, and the wider the range, the more easily the stable spinning is performed. The “devitrification” is the phenomenon that crystals precipitate when the temperature of the molten glass is decreased.
Accordingly, a glass composition has been proposed in which the composition of the glass composition as the raw material for S-glass is improved in such a way that the glass composition includes CaO as well as SiO2, Al2O3 and MgO. As the foregoing glass composition, a glass composition is known which allows the spinning to be easily performed at relatively low temperatures while the working temperature range is being maintained, for example, by decreasing the viscosity on the basis of the decrease of the 1000-poise temperature (see. Patent Literature 1). As the foregoing glass composition, a glass composition is also known in which the difference between the 1000-poise temperature and the liquid phase temperature is large (see, Patent Literature 2).